Anabolic response of mouse bone-marrow-derived stromal cell clone ST2 cells to low-intensity pulsed ultrasound

The effects of 20-min exposure to low-intensity, pulsed ultrasound were inv estigated in ST2 cells of bone marrow stromal origin. They responded to ult rasound with elevated levels of IGF mRNAs, osteocalcin, and bone sialoprote in mRNAs. The upregulated expression of these messages appeared in a biphas ic manner, with the first peak resistant to the protein synthesis inhibitor cycloheximide, and a second peak that was eliminated by NS398, an inhibito r of the inducive prostaglandin G/H synthase (cyclooxygenase-2). A cumulati ve effect of mechanical loading called the memory effect, which has been ob served in vivo, can be explained from such a biphasic anabolic reaction med iated by prostaglandins. The upregulation of IGF or osteocalcin mRNAs can b e observed even at 24 h after the initiation of the 20-min exposure to ultr asound. Our results suggest that this low-intensity, pulsed ultrasound, whi ch has been clinically used to accelerate the healing processes of fracture d bone, induces a direct anabolic reaction of osteogenic cells, leading to bone matrix formation. (C) 2000 Academic Press.